By Karlo Boursard
For any mode of multiplication there is some reality that is signified indeterminately, which is then further determined by some principle distinct from itself.
For example, the generic notion animal signifies all animals, but in an indeterminate way. It stands to be further determined by the addition of a specifying feature or features—e.g., rationality—that is formally distinct from the generic notion.
The same is true for the multiplication of a species into its individual members. The
species human signifies all individuals of its kind, but in an indeterminate way. For the species to be further determined to the individuals, like Plato and Socrates, recourse to another principle besides the species is necessary. That principle is matter.
Pure esse (subsistent being itself) cannot possibly have a potency to be further
determined by something formally distinct from itself. This is because there is nothing other than esse by which it can be determined—except non-being. And to be determined by nothing is not to be determined at all.
Therefore, there can be nothing distinct from pure esse that could possibly determine it in a way that would make multiple instances of it. Pure esse is intrinsically indeterminable, and therefore in principle cannot be multiplied. From this it follows that there can be only one reality of which its nature (essence) is identical to its act of being (existence). There can be only one reality that is ipsum esse subsistens.
Karlo Broussard is a staff apologist and speaker for Catholic Answers. He travels the country giving talks on apologetics, biblical studies, theology, and philosophy, and is a regular guest on the radio program Catholic Answers Live. You can book Karlo for a speaking event by contacting Catholic Answers at 619-387-7200. You can also view Karlo’s videos at karlobroussard.com. A native of Southern Louisiana, Karlo now resides in Southern California with his wife and five children.